If you're looking for a really controlled and good soundig subwoofer, I can recommend this:
http://www.svsound.com/subwoofers/sealed-box/SB13-Ultra
Sounds good and has a nice DSP with more than enough features
http://www.svsound.com/subwoofers/sealed-box/SB13-Ultra
Sounds good and has a nice DSP with more than enough features